sleep in function but not block other functions and code - c++

Question

I am on esp8266 module/microcontroller. I have never wrote in C++. Now I am trying to insert my own small "non blocking" function in one file file. My function should wait 5 seconds on background and then print something. But I don't want to delay whole initialization of meInit() for 5 seconds, it should be let's say parallel "non blocking" function. How is this possible please?
void meInit()
{
if (total > 20) total = 20;
value = EEPROM.read(1);
Serial.begin(115200);
Serial.setTimeout(10);
loadSettings(true);
buildMe();
initFirst();
//here I need to call "non-blocking" function with no delay and process immediatelly further
call5sFunct();
...do other functions here immediatelly without 5s delay...
}
void call5sFunct()
{
Sleep(5000);
DEBUG_PRINTLN("I am back again");
}
P.S. short sample is highly appreciated :) thx

Answer 1

Use std::thread to launch call5sFunct(); in other thread, like this:
//...
initFirst();
//here I need to call "non-blocking" function with no delay and process immediatelly further
std::thread t1(call5sFunct);
t1.detach();
...do other functions here immediatelly without 5s delay...
//...
You need to include #include <thread>

Answer 2

You must not sleep at all, but just call your function after 5 seconds have passed, in the loop function. Something like this (untested):
unsigned long start_time = 0;
bool call5sFunct_executed = false;
void meInit()
{
if (total > 20) total = 20;
value = EEPROM.read(1);
Serial.begin(115200);
Serial.setTimeout(10);
loadSettings(true);
buildMe();
initFirst();
// You cannot call it here, but in loop()
// call5sFunct();
// ...do other functions here immediatelly without 5s delay...
}
void call5sFunct()
{
DEBUG_PRINTLN("I am back again");
}
void loop()
{
unsigned long loop_time = millis();
if (!call5sFunct_executed && (loop_time - start_time >= 5000))
{
call5sFunct();
call5sFunct_executed = true;
}
// .... the rest of your loop function ...
}
However, this template must be used extensively programming microcontrollers. It would be really coumbersome and error-prone to write production code like this - but it's important you get the point.
There are many libraries that make it easy to implement asynchronous operations on arduino, hiding this mechanism. For example take a look to TaskScheduler.
Google for "arduino asynchronous functions" and you will find a lot of alternatives.